Ammonia generating apparatus

ABSTRACT

The invention provides an ammonia generating apparatus which is high in efficiency of heat transfer and compact. The ammonia generating apparatus includes a urea water introducing part, a flow passage for urea water to flow therethrough, and heating means, wherein the flow passage is connected to the urea water introducing part, and the heating means heats urea water present within the flow passage.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to an ammonia generating apparatusfor generating, from urea water, ammonia to be used for NOx removalsystems in boilers or the like.

[0002] In recent years, there has been a demand for further reduction inNOx also for boilers. As one of countermeasures therefor, a method hasbeen taken that a boiler is equipped with a NOx removal system, whereammonia as a reducing agent is added to combustion exhaust gas so thatthe NOx is reduced. Whereas this ammonia is generated by, for example,heating urea water, there is a desire for ammonia generating apparatuseshaving higher efficiency of heat transfer and a compact body.

SUMMARY OF THE INVENTION

[0003] It is therefore an object of the present invention to provide anammonia generating apparatus having a high efficiency of heat transferand being compact.

[0004] In order to achieve the above object, in a first aspect of thepresent invention, there is provided an ammonia generating apparatuscomprising: a urea water introducing part; a flow passage for urea waterto flow therethrough; and heating means, wherein the flow passage isconnected to the urea water introducing part, and the heating meansheats urea water present within the flow passage.

[0005] In a second aspect of the present invention, there is provided anammonia generating apparatus as described in the first aspect, whereinpart of the flow passage is formed into a helical part, and the heatingmeans is placed inside the helical part.

[0006] Now an embodiment of the present invention is described below. Anammonia generating apparatus according to the present invention has aurea water introducing part, a flow passage, and heating means. The ureawater introducing part has an inlet nozzle for introducing urea water.The flow passage is connected to the urea water introducing part, andurea water flows through within the flow passage. The heating means, forheating the urea water within the flow passage to generate ammonia, islocated in proximity to the flow passage. This heating means isimplemented by, for example, an electric heater.

[0007] Part of the flow passage is laid out in a helical shape, and theheating means is placed inside this helical part. By this arrangementand placement, heat emitted from the heating means can be received bythe whole helical part and, as a result, the amount of heat release tooutside is suppressed as much as possible, thus allowing the efficiencyof heat transfer to be improved. Then, by making effective use of aspace formed inside the helical part, the apparatus can be made morecompact in construction as a whole and thus a space-saving apparatus.

[0008] In the flow passage, heat transfer inhibiting means is providedupstream of the helical part. This heat transfer inhibiting meansfunctions to inhibit heat from being transferred from its mountingposition to the upstream side, thereby preventing urea water from beingcrystallized by evaporation of moisture content before its arrival atthe helical part, or preventing occurrences of unnecessary intermediatesfrom the urea water, to a minimum. That is, according to studies by theinventors of the present application, it has been found out that it iswithin a temperature range of about 80-180° C. that crystallization ofurea water or generation of unnecessary intermediates is likely to takeplace. Thus, the heat transfer inhibiting means is so designed as tohave an entrance temperature of not more than 80° C. and an exittemperature of not less than 180° C., while the above temperature rangeoccurs limitedly only to the site where the heat transfer inhibitingmeans is provided. Moreover, the length of the this temperature rangesite is made as short as possible, by which the crystallization of ureawater or the generation of unnecessary intermediates is suppressed to aminimum.

[0009] The heat transfer inhibiting means is implemented by providing amember made of, for example, a material having a large heat insulatingeffect (e.g. ceramics) at a place halfway on the flow passage. The heattransfer inhibiting means may also be designed so that air is introducedfrom outside, where heat transferred from the helical part side iscollected by the air, and the flow of the air that has collected heat isdirected toward the helical part so that the heat is returned to thehelical part.

[0010] The inlet nozzle is equipped with an elastic sealing member insuch a way that injection holes of the inlet nozzle are covered with theelastic sealing member. More specifically, with urea water introduced,when the urea water is pressurized, the elastic sealing member is pushedby pressure, causing the injection holes to be opened, so that the ureawater flows out. Then with the urea water released from pressurization,the elastic sealing member returns to the original position, causing theinjection holes to be closed. Consequently, while the urea water is notbeing introduced, the injection holes are sealed by the elastic sealingmember and therefore the urea water remaining in the inlet nozzle isnever crystallized by the evaporation of moisture content, ensuring theprevention of blockage of the inlet nozzle. In addition, the elasticsealing member is made of, for example, synthetic rubber.

[0011] An air supply line is connected to the urea water introducingpart. Air supplied along this air supply line functions to convey ureawater in the flow passage, and to blow out urea water deposited on theinlet nozzle. Accordingly, supplying air through the air supply lineprevents the urea water from residing, as it is deposited, within theurea water introducing part and the flow passage.

[0012] Further, in this ammonia generating apparatus, a cleaning fluidsupply line for cleaning the interior of the flow passage is provided.This cleaning fluid supply line is connected to the upstream side of theheat transfer inhibiting means so that even if part of the urea water iscrystallized, the crystallized urea water can be cleaned. As thecleaning fluid, water, vapor or the like is used.

[0013] As shown above, according to this constitution, the ammoniagenerating apparatus allows continuous heating to be performed whileurea water is kept flowing, so that the efficiency of heat transfer canbe greatly improved. That is, since urea water flows at a specified flowrate in the flow passage, the resulting efficiency of heat transfer isgreatly improved, as compared with the case in which heating is donewith the urea water residing in the tank. Besides, as compared with thecase of heating with the urea water residing in the tank, the rise timefrom when urea water begins to be supplied to when a steady-stategeneration of ammonia is reached can be shortened, and the heatingcapacity of the heating means can be reduced. Further, the ammoniagenerating apparatus can be reduced in size as a whole, and inparticular, with the heating means placed inside the helical part, theammonia generating apparatus can be made more compact in structure.

[0014] In addition, the heating means may be provided either outside thehelical part or both inside and outside thereof. The heating means mayalso be provided so as to surround the entire circumferential peripheryof the flow passage along the flow passage.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015]FIG. 1 is a longitudinal sectional explanatory view of a firstembodiment of the invention;

[0016]FIG. 2 is an enlarged longitudinal sectional explanatory viewshowing details of the urea water nozzle in FIG. 1;

[0017]FIG. 3 is an enlarged longitudinal sectional explanatory viewshowing details of the heat transfer inhibiting means in FIG. 1;

[0018]FIG. 4 is a longitudinal sectional explanatory view of a secondembodiment of the invention; and

[0019]FIG. 5 is an enlarged longitudinal sectional explanatory viewshowing another embodiment of the heat transfer inhibiting means as asubstitute for that of FIG. 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] Hereinbelow, concrete embodiments of the present invention aredescribed in detail based on the accompanying drawings. First, a firstembodiment shown in FIGS. 1-3 is described.

[0021] The ammonia generating apparatus according to the presentinvention is designed to generate ammonia by heating urea water and, asshown in FIG. 1, has a urea water introducing part 1, where a flowpassage 2 for urea water to flow therethrough is connected to the bottomof this urea water introducing part 1. The urea water introducing part 1has an inlet nozzle 3 provided so as to be directed downward, and an airsupply line 4 is connected to a side face of the urea water introducingpart 1. This air supply line 4 is connected so as to be opposed to theforefront of the inlet nozzle 3, and air supplied along the air supplyline 4 functions to convey urea water in the flow passage 2 and to blowout urea water deposited at the forefront of the inlet nozzle 3. Inaddition, the air supply line 4 may also be connected to the top face ofthe urea water introducing part 1 in parallel to the inlet nozzle 3.

[0022] Part of the flow passage 2 is laid out into a helical shape,forming a helical part 5, which is fixed to a cylindrical member 6 inclose contact with the outer circumferential surface of the cylindricalmember 6. Inside the cylindrical member 6, an electric heater as heatingmeans 7 is provided at a specified spacing to the inner circumferentialsurface of the cylindrical member 6. Also, a temperature sensor 8 isprovided in the space between the cylindrical member 6 and the heatingmeans 7, and by detecting surface temperature of the heating means 7with this temperature sensor 8, electric energy to be supplied to theheating means 7 is controlled by a controller 9 so that the surfacetemperature of the heating means 7 becomes about 500° C. Accordingly,the urea water is heated by the heating means 7 while flowing within thehelical part 5, by which gaseous ammonia is generated continuously.Further, outside the helical part 5, a heat insulating material 10 isprovided so as to cover the entire helical part 5.

[0023] The flow passage 2 is so formed that its upstream side of thehelical part 5 is slightly slanted in order to prevent the residence ofurea water, and heat transfer inhibiting means 11 is provided at aspecified position on this upstream side. This heat transfer inhibitingmeans 11 functions to inhibit heat from being transferred from itslocation to the upstream side, thereby inhibiting urea water from beingcrystallized by evaporation of moisture content before its arrival atthe helical part 5, or inhibiting occurrences of unnecessaryintermediates from the urea water, to a minimum.

[0024] The urea water introducing part 1 is so formed as to be larger indiameter than the flow passage 2, their junction portion being tapereddownwardly so that the urea water does not accumulate.

[0025] Further, the flow passage 2 is connected at its downstream sideend portion to a NOx removal system (not shown) provided in the boileror the like, so that ammonia generated in the helical part 5 is suppliedcontinuously to the NOx removal system.

[0026] Next, construction of the inlet nozzle 3 is described in detailwith reference to FIG. 2. As shown in FIG. 2, a plurality of injectionholes 12, 12, . . . are provided on the side wall of the inlet nozzle 3on its front end side. Besides, a tubular elastic sealing member 13 isattached so as to cover these injection holes 12. More specifically, theelastic sealing member 13 is made of, for example, synthetic rubber, andwhen urea water is pressurized upon its introduction, the elasticsealing member 13 is pushed by the pressure, causing the injection holes12 to be opened, so that the urea water flows out through between theouter circumferential surface of the inlet nozzle 3 and the innercircumferential surface of the elastic sealing member 13. When the ureawater is released from pressurization, the elastic sealing member 13returns to the original position, causing the injection holes 12 to beclosed. In this connection, FIG. 2 shows a state in which the urea wateris flowing out.

[0027] Therefore, with the elastic sealing member 13 provided, while theurea water is not being introduced, the injection holes 12 are sealedand closed by the elastic sealing member 13, thus preventing theoccurrence that urea water remaining in the inlet nozzle 3 iscrystallized by the evaporation of moisture content, and so ensuring theprevention of blockage of the inlet nozzle 3.

[0028] Next, construction of the heat transfer inhibiting means 11 isdescribed in detail with reference to FIG. 3. As shown in FIG. 3, theheat transfer inhibiting means 11 is so constituted that the flowpassage 2 is intercepted halfway with the upstream-side end portion ofthe downstream-side flow passage 2 larger in diameter than thedownstream-side end portion of the upstream-side flow passage 2, wherethe two parts are concentrically overlapped with each other over aspecified length and a heat insulating material 14 made of ceramics orthe like is provided therebetween. Therefore, heat transferred from thehelical part 5 along the flow passage 2 is inhibited by the heatinsulating material 14 from being further transferred to the upstreamside.

[0029] Also, the heat transfer inhibiting means 11 is so designed thattemperature of A point, which is the entrance point, will be not morethan 80° C. while temperature of B point, which is the exit point, willbe not less than 180° C. That is, a temperature range of about 80-180°C., which is more likely to cause crystallization of urea water orgeneration of unnecessary intermediates, is limited to the site wherethe heat transfer inhibiting means 11 is provided, while the length ofthis temperature range site is made as short as possible. Thus, thecrystallization of urea water or the generation of unnecessaryintermediates is suppressed to a minimum.

[0030] With such a constitution as described above, now its operation isdescribed. From the inlet nozzle 3, about 20% concentration urea wateris supplied at a flow rate of about 10 milliliters/min., and this ureawater is conveyed within the flow passage 2 by air (flow rate: about 30liters/min.) coming through the air supply line 4, thus the urea waterair reaching the helical part 5. Then, the urea water, while flowingthrough within the helical part 5, is heated to about 200-500° C. by theheating means 7, by which ammonia is generated. The resultant ammonia issupplied to the NOx removal system (not shown).

[0031] Therefore, according to the above constitution, urea water can becontinuously heated while flowing at a flow rate, so that the efficiencyof heat transfer is greatly improved. Also, because of a small contentof urea water within the helical part 5, the rise time from when theurea water begins to be supplied until when a steady-state generation ofammonia is reached is shortened, and besides the heating capacity of theheating means 7 can be reduced. Also, because of the provision of theheating means 7 inside the helical part 5, the amount of heat release tooutside is suppressed as much as possible, and besides the wholeapparatus is compact in structure. Further, because of the provision ofthe heat transfer inhibiting means 11 and the elastic sealing member 13,the crystallization of urea water and the generation of unnecessaryintermediates are suppressed to a minimum.

[0032] For intermittent generation of ammonia, the supply of urea waterfrom the inlet nozzle 3 is controlled to an intermittent one in responseto a request signal for ammonia generation. In this case, the air fromthe air supply line 4 is supplied at a specified amount continuouslyeven while the supply of urea water keeps halted, so that the urea waterdoes not reside within the flow passage 2. Further, with the supply ofurea water halted, the heating means 7 also continues operating so thatthe temperature of the helical part 5 is maintained at a specifiedtemperature. Accordingly, while the ammonia generation is halted,neither the crystallization of urea water nor the generation ofunnecessary intermediates occurs in the helical part 5, so that thegeneration of a specified amount of ammonia can be started immediatelyupon resumption of ammonia generation.

[0033] In this connection, for cleaning of the interior of the flowpassage 2, it is also possible to supply water as a cleaning fluid fromthe air supply line 4 instead of air, and to thereby clean the interiorof the flow passage 2, while no ammonia is generated with the supply ofurea water halted. That is, the air supply line 4 is made to serve as acleaning fluid supply line. The supplied cleaning fluid cleans away theremaining urea water or its crystallized matters in the urea waterintroducing part 1 and the flow passage 2, and discharges them outsidevia a discharge line (not shown). Also, supply of the cleaning fluid maybe controlled so as to be effected when a blockage within the flowpassage 2 is detected. Furthermore, the cleaning fluid supply line maybe provided separately from the air supply line 4, and connected to theupstream side of the heat transfer inhibiting means 11 where thecrystallization of urea water is more likely to occur.

[0034] For the heating of urea water by the heating means 7, it has beenarranged that the helical part 5 is previously heated by the heatingmeans 7 before supplying the urea water, so that the interior of thehelical part 5 is heated up to a specified temperature in advance.However, there is a time delay until the flow passage 2 between the heattransfer inhibiting means 11 and the helical part 5 is heated up to aspecified temperature. Therefore, during the time interval, thecrystallization of urea water or the generation of unnecessaryintermediates is more likely to occur in the flow passage 2 between theheat transfer inhibiting means 11 and the helical part 5. Thus, it isalso possible to pre-heat the flow passage 2 between the heat transferinhibiting means 11 and the helical part 5 by supplying humidified air(temperature: about 350° C.) to part of the flow passage 2 immediatelydownstream of the heat transfer inhibiting means 11.

[0035] Next, a second embodiment as shown in FIG. 4 is described, wherethe same constituent members as those of the foregoing first embodimentare designated by the same reference numerals and their detaileddescription is omitted. In this second embodiment, inside thecylindrical member 6, a threaded member 15 is inserted and the helicalpart 5 is formed. More specifically, the threaded member 15 is formedinto a trapezoidal thread, where a screw thread with a trapezoidal crosssection is formed at the outer circumferential surface of the threadedmember 15, the top of this screw thread is in contact with the innercircumferential surface of the cylindrical member 6, and the threadgroove forms the flow passage 2. Also, an insertion hole 16 forinserting the heating means 7 is provided inside the threaded member 15.

[0036] According to this second embodiment, since the helical part 5 isformed only by inserting the threaded member 15 into the cylindricalmember 6, assembly work becomes simpler and the number of assemblyman-hours is reduced. Also, even upon occurrence of blockage within thehelical part 5 due to the crystallization of urea water, the threadedmember 15 can be pulled out and removed, and the outer circumferentialsurface of the threaded member 15 and the inner circumferential surfaceof the cylindrical member 6 can be cleaned with great ease.

[0037] Further, another embodiment of the heat transfer inhibiting means11 is described with reference to FIG. 5. The heat transfer inhibitingmeans 11 shown in FIG. 5 has a so-called ejector structure, where air isintroduced from outside, and heat that has been transferred from thehelical part 5 side is collected by the air, and a flow of the air thathas collected the heat is directed toward the helical part 5, by whichheat is returned to the helical part 5. That is, part of the flowpassage 2 is formed into a double-cylindrical structure comprising anouter cylindrical part 17 and an inner cylindrical part 18. A specifiednumber of air inlet holes 19, 19, . . . are formed in the outercylindrical part 17 along its periphery, a front-end opening 20 of theinner cylindrical part 18 is placed inside a tapered portion 21 in thedownstream-side end portion of the outer cylindrical part 17, and anannular flow port 22 is formed therebetween. In addition, theupstream-side end portion of the outer cylindrical part 17 is closed.

[0038] Accordingly, when the air accompanied by urea water passesthrough the front-end opening 20, outside air is sucked up through theflow port 22 via the air inlet holes 19. Then, heat that has beentransferred from the helical part 5 to the outer cylindrical part 17 iscollected by inflow outside air so as to return to the helical part 5,thus inhibiting the heat from being transferred to the inner cylindricalpart 18. Also, the heat transfer inhibiting means 11 is so designed, asthat shown in FIG. 3, that the temperature of A point, which is theentrance, will be not more than 80° C., and that the temperature of Bpoint, which is the exit, will be not less than 180° C. That is, atemperature range of about 80-180° C., which is more likely to causecrystallization of urea water or generation of unnecessaryintermediates, is limited to the site where the heat transfer inhibitingmeans 11 is provided, while the length of this temperature range site ismade as short as possible. Thus, the crystallization of urea water orthe generation of unnecessary intermediates is suppressed to a minimum.

[0039] In addition, the heat transfer inhibiting means 11 shown in FIG.5 can be used either in the first embodiment or in the secondembodiment.

[0040] According to the present invention, urea water can becontinuously heated while flowing, so that the efficiency of heattransfer can be greatly improved. Besides, the size of the ammoniagenerating apparatus can be downsized as a whole and, in particular,with the heating means provided inside the helical part in the flowpassage, the ammonia generating apparatus can be formed more compact instructure.

What is claimed is:
 1. An ammonia generating apparatus comprising: aurea water introducing part; a flow passage for urea water to flowtherethrough; and heating means, wherein the flow passage is connectedto the urea water introducing part, and the heating means heats ureawater present within the flow passage.
 2. The ammonia generatingapparatus as claimed in claim 1 , wherein part of the flow passage isformed into a helical part, and the heating means is placed inside thehelical part.